1. Field of the Invention
The present invention relates to conveyance control of a print medium. Especially, the present invention relates to a configuration for detecting an origin or phase of a conveying roller at the time of its rotation and a method for the same in a configuration of conveying the print medium using the conveying roller.
2. Description of the Related Art
In printing apparatuses in recent years, there is increased printing use of printing photographic images not only on plain papers but also on special purpose papers. In particular, in the ink jet printing apparatus, a trend of a decreased size of an ink drop has progressed and it has become possible to output an image comparative to or better than silver salt photographs with high resolution. With realization of such high resolution of images, higher precision of paper conveyance is also being advanced and there have been proposed a lot of methods whereby the conveying roller such that a metallic shaft is coated with grinding stone is used and methods for controlling conveyance of such a conveying roller with high precision.
For example, Japanese Patent Laid-Open No. 2006-240055 discloses a configuration where a code wheel is provided on the same axis of the conveying roller and slits formed on its circumferential part at equal intervals are detected by an encoder sensor fixed in the apparatus. According to this, a technology of performing drive control of a DC motor for rotating the conveying roller depending on a cycle at which the slits are detected, etc., is disclosed. Then, according to the same document, a method includes acquiring an origin of the conveying roller by having provided a pattern for rotation phase detection, separately from the slits on the code wheel, and detecting the pattern concerned with another sensor in order to correct a conveyance error resulting from eccentricity of the conveying roller.
FIG. 20 is a sectional view for explaining an installation state of the code wheel and the sensors. A film-like code wheel 2002 shares a rotation axis with a conveying roller 2001 and is disposed around its circumference in a spreading manner. Slits 2002a that are arranged at equal intervals and are used for detection of positional precision and a belt-like pattern 2002b used for phase detection of roller rotation are printed on the code wheel 2002. An encoder sensor 2003 is installed at a position where the slits 2002a pass with rotation of the code wheel 2002, and detects a rotation amount of the code wheel 2002, i.e., the conveying roller 2001. On the other hand, an edge sensor 2004 detects the edge of the pattern 2002b that moves with the rotation of the code wheel 2002, and the printing apparatus is configured to be able to set the origin of the roller rotation using this detected timing.
FIG. 21 is a diagram showing another example of a configuration for detecting the origin of the conveying roller. In this example, a sensed part 2102 is attached to a part of the conveying roller 2101, and moves in a circle with rotation of the conveying roller 2101. A photo-interrupter 2103 is being fixed at a position where the sensed part 2102 in the apparatus passes and can detect the origin of the conveying roller 2101 from a timing at which the sensed part 2102 intercepts the photo-interrupter 2103.
Thus, in order to perform the conveyance control in a high-precision state while correcting the conveyance error resulting from the eccentricity of the conveying roller, a mechanism for detecting the origin of the conveying roller also becomes necessary, apart from the mechanism for detecting the rotation amount of the conveying roller.
However, since the above-mentioned conventional configuration requires some electronic device elements, such a photo-interrupter for phase detection, and cable wiring for this newly, a cost of the apparatus cannot avoid increasing.